Broadband communication networks are used in a variety of high speed application services such as internet access, video conferencing, video on demand, and interactive TV. Although fiber optic cable is the preferred transmission media for such high data rate services, the lack of fiber optic cables in existing networks and the prohibitive costs of installing such optical networks have led telephone companies around the world to include existing twisted-pair loops in their next generation broadband access networks. Because current telephone wiring connections were not designed to support high speed data communications, technologies were developed to increase the transmission capabilities of existing telephone wiring. One technology for providing such high data rate services on existing twisted-pair connections is Asymmetrical Digital Subscriber Line (ADSL). ADSL transfers data over the higher frequencies in the twisted-pair copper wires that currently connect most homes and businesses. ADSL accomplishes this by increasing the transmission capabilities of the current telephone wiring connections. Another technology for providing high data rate services is Very high rate Digital Subscriber Line (VDSL). VDSL transmits high speed data over short reaches of twisted-pair copper telephone lines, with a range of speeds depending upon actual line length. Thus, both ADSL and VDSL technology enable data to be exchanged over the twisted-pair copper wires at much higher speeds than conventional modems and analogue lines.
To increase bandwidth capacity on existing twisted pair connections, ADSL and VDSL systems have adopted discrete multi-tone (DMT) modulation. DMT is a multiple carrier technique that divides the available bandwidth of a communications channel into a number of sub-channels, also referred to as carriers or bins. By working with a large number of carriers rather than a single carrier, the available channel capacity is maximized thereby optimizing performance of the transmission. Once a connection between two modems has been established, the modems continue to monitor the changing signal-to-noise ratios on the line and swap bits from one carrier to another to maintain system performance.
Current DMT modulation modems have several disadvantages. Traditionally, in DMT related modems, up to 4096 carriers may be used to transport bits. Different parameters relating to each individual carrier are stored and used for modem operations. Examples of the various parameters needed for modem operation include the gain, the number of bits that can be loaded onto each carrier (i.e. bit loading), and the signal-to-noise ratio (“SNR”) of each carrier. One disadvantage of current DMT modulation systems is the consumption of large amounts of memory space required to store all these parameters for each individual carrier. Consequently, as the number of carriers increases, so does the amount of memory space required to store the parameters relating to each individual carrier.
Another disadvantage with current DMT systems is the amount of processing time required during the initialization phase of the modems. DMT modulation requires that the far-end transmitting modem be informed of the transmission channel response, such as bit loading and gain information for each carrier. Thus, the initialization time of current DMT systems with multiple carriers is long due to the significant amounts of memory required for storing all the parameters for each individual carrier and to the size and number of message transmissions between modems during the initialization phase.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with the present invention as set forth in the remainder of the present application with reference to the drawings.
It is an object of the present invention to solve the aforementioned problems by providing a system and method for grouping carriers in multi-carrier systems.